Static electricity buildup in carpets and textiles made of synthetic fibrous polymers has long been an inconvenience. With today's widespread use of computers, it has become a more serious problem. Static electricity buildup followed by discharge can damage computer circuits and destroy information stored in computer memory. By adding a conductive fiber to carpet yarn, the buildup of static electricity is overcome. The problem then becomes producing the conductive fiber.
Two of the most widely produced conductive filaments are coated filaments and bicomponent filaments, with coated fibers generally having the greater conductivity. There have been many approaches of coating filaments to make them conductive, including suffusion coating.
Exemplary of patents describing the production of conductive synthetic filaments is U.S. Pat. No. 4,085,182 to Kato, which describes a process for making sheath/core filaments. The Kato filament has a conductive core.
Sometimes it is desirable to ply one or more conductive filaments with non-conductive filaments to provide support to the conductive filament for later end uses. Such a plied yarn is known as supported yarn. Supported conductive yarn is useful, for example, when inserting the conductive filament in carpet yarn.
Co-extrusion of conductive filaments with non-conductive filaments appears to be shown in French Pat. Publication No. 2466517 (FIGS. 1-6). One advantage of using supported conductive yarn for end uses is that the supported yarn can be conventionally dyed, masking the dark color of conductive filaments made conductive by use of dark materials like carbon. Since the conductive filament is an integral part of the yarn bundle, another advantage of supported conductive yarn is improved downstream performance during knitting, weaving or insertion into carpet yarn.
Insertion of conductive filaments into non-conductive yarn is known. Previously spun and wound-up conductive filaments may be combined with one or more freshly spun, non-conductive filaments to make bulked continuous filament yarn which is antistatic. Exemplary are U.S. Pat. No. 4,612,150 to De Howitt and U.S. Pat. No. 4,997,712 to Lin. Both of these patents described processes for combining previously spun conductive filaments with freshly spun non-conductive filaments followed by co-drawing and co-bulking. The insertion of wound-up filaments into freshly spun filaments requires extra bobbins and labor when making conductive yarn.
Individual previously spun and wound up filament sets may be combined immediately after the carbon suffusion of one set. See, for example, U.S. Pat. No. 4,545,835 to Gusack et al.
Making supported conductive yarns by insertion of a conductive feed yarn according to known methods is fairly burdensome and labor intensive, in that separate processes are required. One process is needed for making the conductive filament for insertion and another process for inserting the wound-up conductive yarn to a spinning process. In addition, known methods for insuring interweaving of the conductive filament are not always as efficient as desired.
It is known to differentially treat separate bundles of freshly spun yarn followed by recombination of the two separately treated bundles. For example, U.S. Pat. No. 3,423,809 to Schmitt describes a process for combining two separately spun and treated filament bundles which are annealed under separate conditions and then recombined to produce a non-conductive yarn having differential shrinkage.
U.S. Pat. No. 3,955,952 to Drummond describes a method for forming a slubby glass fiber by subjecting separate groups of freshly spun glass fibers to differential velocity prior to combination.
U.S. Pat. No. 4,153,660 to Reese describes a process for producing differential shrinkage in yarns when heated. The differential shrinkage is due to the application of different finishes to two different freshly spun filament bundles, which are then combined.
Yet, there is no known process for making a supported conductive yarn in a self-contained process. Such a one-step process would provide several advantages over the state of the art. Some of these advantages are the elimination of the production, packaging, and storage of feed yarn packages; improved coating performance; elimination of other sources for feed yarn; deniers and filament counts can be easily changed; improved control of conductive or support yarn properties; and reduction in the manpower needed to prepare an antistatic yarn. Another aspect of such a process includes presentation to the suffusion coater of a yarn having constant tension. This allows higher speeds than available with high and erratic backwinding tensions.